Question

Докажите тождество: 1) (2а + b)3 - (a - b)2(8a + b) = 27a2b; 3) (5х + y)3 - y(5х - у)2 – 25x(x+y)2 = 100х3; 4) 5(х - у)3 + 5y(x+y)2 - х(х - 5y)2 = 4х3. ​

Answer 1

Ответ:

(2a+b)³-(a-b)²(8a+b)=8a³+6a²b+6ab²+b³-(a²-2ab+b²)(8a+b)=8a³+6a²b+6ab²+b³-(8a³-16a²b+8ab²+a²b-2ab²+b³)=8a³+6a²b+6ab²+b³-(8a³-15a²b+6ab²+b³)=8a³+6a²b+6ab²+b³-8a³+15a²b-6ab²-b³=21a²b

21a²b≠27a²b

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